Head mounted displays (HMDs), which are used while worn on the head to place a video screen in front of each eye of the user, find applications in various fields including the field of virtual reality. Typical HMDs are designed in the shape of a frame of goggles or large glasses that block out outside light and force the user to see only the HMD's pictures. With an HMD used, the user can view images irrespective of the direction he or she faces but then again it gives the user visual isolation from the surrounding environment.
In recent years, small image display devices have been proposed that allow users to view both images and the surrounding environment by means of presenting the images in a certain part of the field of vision.
The image display device of this type is disclosed in, for example, Japanese patent laid-open document (JP-A-7-209600). This image display device has a liquid crystal display (LCD), a reflecting mirror, an ocular lens and other components contained within a single housing. The housing has a clip attached thereto. This clip is used for mounting the image display device onto a glasses or sunglasses frame. The housing is placed on top of either right or left lens of the glasses over the outside surface of it. An image that is displayed on the LCD is directed to one eye of the user in a diagonal down direction through the reflecting mirror, the ocular lens, and the lens of the glasses.
The image display device of this type provides the user with a choice between seeing the surrounding environment and seeing images by the movement of the eyes. It has a high value in terms of its availability in everyday life at any place both inside and outside a building.
This image display device has, however, something to be improved.
The reason is that images are seen with only one eye in this image display device. Seeing images with one eye often triggers user eyestrain and places a heavy burden on the beholding user. Therefore, this image display device is not suited for use for prolonged periods of time.
A possible solution to the aforementioned problem is to develop an image display device having a pair of display means: right-eye display means and left-eye display means.
However, the distance between both eyes and the vision of a person vary among individuals. Even with an image display device having two display means, a mismatch between the user and the two display means can cause eyestrain of the user.
There has been no image display device of the type that presents images in a certain part of the field of vision in which the image display device solves the aforementioned problems and gives a user the opportunity of its use for prolonged periods of time, sometimes of a long-time viewing of images.
An object of the present invention is to provide an image display device of the type that presents images in a certain part of the field of vision in which the image display device can be used for prolonged periods of time.